MRI surveillance for the detection of local recurrence in rectal cancer after transanal endoscopic microsurgery

Post-Surgical Imaging Assessment in Rectal Cancer: Normal Findings and Complications

Rectal cancer (RC) is one of the deadliest malignancies worldwide. Surgery is the most common treatment for RC, performed in 63.2% of patients. The type of surgical approach chosen aims to achieve maximum residual function with the lowest risk of recurrence. The selection is made by a multidisciplinary team that assesses the characteristics of the patient and the tumor. Total mesorectal excision (TME), including both low anterior resection (LAR) and abdominoperineal resection (APR), is still the standard of care for RC. Radical surgery is burdened by a 31% rate of major complications (Clavien-Dindo grade 3-4), such as anastomotic leaks and a risk of a permanent stoma. In recent years, less-invasive techniques, such as local excision, have been tested. These additional procedures could mitigate the morbidity of rectal resection, while providing acceptable oncologic results. The "watch and wait" approach is not a globally accepted model of care but encouraging results on selected groups of patients make it a promising strategy. In this plethora of treatments, the radiologist is called upon to distinguish a physiological from a pathological postoperative finding. The aim of this narrative review is to identify the main post-surgical complications and the most effective imaging techniques.

MRI anatomy of the rectum: key concepts important for rectal cancer staging and treatment planning

A good understanding of the MRI anatomy of the rectum and its surroundings is pivotal to ensure high-quality diagnostic evaluation and reporting of rectal cancer. With this pictorial review, we aim to provide an image-based overview of key anatomical concepts essential for treatment planning, response evaluation and post-operative assessment. These concepts include the cross-sectional anatomy of the rectal wall in relation to T-staging; differences in staging and treatment between anal and rectal cancer; landmarks used to define the upper and lower boundaries of the rectum; the anatomy of the pelvic floor and anal canal, the mesorectal fascia, peritoneum and peritoneal reflection; and guides to help discern different pelvic lymph node stations on MRI to properly stage regional and non-regional rectal lymph node metastases. Finally, this review will highlight key aspects of post-treatment anatomy, including the assessment of radiation-induced changes and the evaluation of the post-operative pelvis after different surgical resection and reconstruction techniques.

Features on Endoscopy and MRI after Treatment with Contact X-ray Brachytherapy for Rectal Cancer: Explorative Results

After neoadjuvant (chemo)radiotherapy for rectal cancer, contact X-ray brachytherapy (CXB) can be applied aiming at organ preservation. This explorative study describes the early features on endoscopy and MRI after CXB. Patients treated with CXB following (chemo)radiotherapy and a follow-up of ≥12 months were selected. Endoscopy and MRI were performed every 3 months. Expert readers scored all the images according to structured reporting templates. Thirty-six patients were included, 15 of whom obtained a cCR. On endoscopy, the most frequently observed feature early in follow-up was an ulcer, regardless of whether patients developed a cCR. A flat, white scar and tumor mass were common at 6 months. Focal tumor signal on T2W-MRI and mass-like high signal on DWI were generally absent in patients with a cCR. An ulceration on T2W-MRI and "reactive" mucosal signal on DWI were observed early in follow-up regardless of the final tumor response. The distinction between a cCR and a residual tumor generally can be made at 6 months. Features associated with a residual tumor are tumor mass on endoscopy, focal tumor signal on T2W-MRI, and mass-like high signal on DWI. Early recognition of these features is necessary to identify patients who will not develop a cCR as early as possible.

Prognosis of Patients Over 60 Years Old With Early Rectal Cancer Undergoing Transanal Endoscopic Microsurgery – A Single-Center Experience

Aim

Transanal endoscopic microsurgery (TEM) is widely performed in early rectal cancer. This technique offers greater organ preservation and decreases the risk of subsequent surgery. However, postoperative local recurrence and distant metastasis remain challenges for patients with high-risk pathological factors. This single-center study reports the prognosis of early rectal cancer patients over 60 years old after TEM.

Methods

The data of the patients over 60 years old who underwent local anal resection were collected retrospectively. Moreover, the 5-year follow-up data were analyzed to determine the 5-year DFS and OS.

Results

47 early rectal cancer patients over 60 years old underwent TEM. There were 27 patients with high-risk factors and 20 patients without high-risk factors. Two patients underwent radical surgery after TEM and ten patients received adjuvant treatment. Local recurrence occurred in 7 patients, of which 4 underwent salvage surgery. The 5-year progression-free survival rate was 75.6%, which was lower in the high-risk patients group (69.6%) than in the non-high-risk patients group (83.3%) (P>0.05). The 5-year OS was 90.2%, but there was no statistically significant difference between the two groups (high-risk patients 87.0%, non-high-risk patients 94.4%). Furthermore, there was no significant difference in DFS and OS between people over and under 70 years old.

Conclusion

Some high-risk factor patients over 60 years old do not have inferior 5-year DFS and OS to the non-high-risk patients. TEM is an option for old patients with high surgical risks. Even if postoperative pathology revealed high-risk factors, timely surgical treatment after local recurrence would be beneficial to improve the 5-year DFS and OS.

Locally recurrent rectal cancer: what the radiologist should know

Despite advances in surgical techniques and chemoradiation therapy, recurrent rectal cancer remains a cause of morbidity and mortality. After successful treatment of rectal cancer, patients are typically enrolled in a surveillance strategy that includes imaging as studies have shown improved prognosis when recurrent rectal cancer is detected during imaging surveillance versus based on development of symptoms. Additionally, patients who experience a complete clinical response with chemoradiation therapy may elect to enroll in a "watch-and-wait" strategy that includes imaging surveillance rather than surgical resection. Factors that increase the likelihood of recurrence, patterns of recurrence, and the imaging appearances of recurrent rectal cancer are reviewed with a focus on CT, PET CT, and MR imaging.

Diffusion-weighted imaging in rectal cancer: current applications and future perspectives

This review summarizes current applications and clinical utility of diffusion-weighted imaging (DWI) for rectal cancer and in addition provides a brief overview of more recent developments (including intravoxel incoherent motion imaging, diffusion kurtosis imaging, and novel postprocessing tools) that are still in more early stages of research. More than 140 papers have been published in the last decade, during which period the use of DWI have slowly moved from mainly qualitative (visual) image interpretation to increasingly advanced methods of quantitative analysis. So far, the largest body of evidence exists for assessment of tumour response to neoadjuvant treatment. In this setting, particularly the benefit of DWI for visual assessment of residual tumour in post-radiation fibrosis has been established and is now increasingly adopted in clinics. Quantitative DWI analysis (mainly the apparent diffusion coefficient) has potential, both for response prediction as well as for tumour prognostication, but protocols require standardization and results need to be prospectively confirmed on larger scale. The role of DWI for further clinical tumour and nodal staging is less well-defined, although there could be a benefit for DWI to help detect lymph nodes. Novel methods of DWI analysis and post-processing are still being developed and optimized; the clinical potential of these tools remains to be established in the upcoming years.

A systematic review and meta-analysis of pT2 rectal cancer spread and recurrence pattern: Implications for target design in radiation therapy for organ preservation

BACKGROUND

There are no guidelines on clinical target volume (CTV) delineation for cT2 rectal cancer treated with organ preservation.

MATERIALS AND METHODS

A systematic review and meta-analysis were performed to determine the extent of distal mesorectal (DMS) and distal intramural spread (DIS), the risk of lateral lymph node (LLN) metastases in pT2 tumours, and regional recurrence pattern after organ preservation.

RESULTS

The rate of DMS > 1 cm was 1.9% (95% CI: 0.4-5.4%), maximum extent: 1.3 cm. The rate of DIS > 0.5 cm was 4.7% (95% CI: 1.3-11.5%), maximum extent: 0.8 cm. The rate of LLN metastases was 8.2% (95% CI: 6.7-9.9%) for tumours below or at peritoneal reflexion and 0% for higher tumours. Regional nodal recurrences alone were recorded in 1.0% (95% CI: 0.5-1.7%) of patients after watch-and-wait and in 2.1% (95% CI: 1.2-3.4%) after preoperative radiotherapy and local excision. Thus, the following rules for CTV delineation are proposed: caudal border 1.5 cm from the tumour to account for DMS or 1 cm to account for DIS, whichever is more caudal; cranial border at S2/S3 interspace; inclusion of LLN for tumours at or below peritoneal reflexion. A planning study was performed in eight patients to compare dose-volume parameters obtained using these rules to that obtained using current guidelines for advanced cancers. The proposed rules led to a mean 18% relative reduction of planning target volume, which resulted in better sparing of organs-at-risk.

CONCLUSION

This meta-analysis suggests a smaller CTV for cT2 tumours than the current guidelines designed for advanced cancers.

Response assessment after (chemo)radiotherapy for rectal cancer: Why are we missing complete responses with MRI and endoscopy?

PURPOSE

To evaluate what features on restaging MRI and endoscopy led to a false clinical diagnosis of residual tumour in patients with a pathological complete response after rectal cancer surgery.

METHODS

Patients with an unrecognized complete response after (chemo)radiotherapy were selected in a tertiary referral centre for rectal cancer treatment. An unrecognized complete response was defined as a clinical incomplete response at MRI and/or endoscopy with a pathological complete response of the primary tumour after surgery. The morphology of the tumour bed and the lymph nodes were evaluated on post-CRT T2-weighted MRI (T2-MRI) and diffusion weighted imaging (DWI). Post-CRT endoscopy images were evaluated for residual mucosal abnormalities. MRI and endoscopy features were correlated with histopathology.

RESULTS

Thirty-six patients with an unrecognized complete response were included. Mucosal abnormalities were present at restaging endoscopy in 84%, mixed signal intensity on T2-MRI in 53%, an irregular aspect of the former tumour location on T2-MRI in 69%, diffusion restriction on DWI in 51% and suspicious lymph nodes in 25%.

CONCLUSIONS

Overstaging of residual tumour after (chemo)radiotherapy in rectal cancer is mainly due to residual mucosal abnormalities at endoscopy, mixed signal intensity or irregular fibrosis at T2-MRI, diffusion restriction at DWI and residual suspicious lymph nodes. Presence of these features is not definitely associated with residual tumour and in selected cases an extended waiting interval can be considered.

FDG-PET/MRI in patients with pelvic recurrence of rectal cancer: first clinical experiences

OBJECTIVES

To determine the value of ¹⁸F-FDG-PET/MRI in the diagnosis and management of patients with pelvic recurrence of rectal cancer.

METHODS

Forty-four patients (16 women, 28 men) with a history of rectal cancer who received FDG-PET/MRI between June 2011 and February 2017 at our institution were retrospectively enrolled. Three patients received two FDG-PET/MRIs; thus a total of 47 examinations were included. Pelvic recurrence was confirmed either with histology (n = 27) or imaging follow-up (n = 17) (> 4 months). Two readers (one radiologist, one nuclear medicine physician) interpreted the images in consensus. Pelvic lesions were assessed regarding FDG uptake and morphology. Sensitivity, specificity, positive and negative predictive values as well as accuracy of PET/MRI in detecting recurrence were determined.

RESULTS

In 47 FDG-PET/MRIs 30 suspicious pelvic lesions were identified, 29 of which were malignant. Two patients underwent resection and had histologically proven pelvic recurrence without showing suspicious findings on FDG-PET/MRI. Changes in management due to FDG-PET/MRI findings had been implemented in eight patients. Eighty per cent (16/20) of resected patients had histologically negative resection margins (R0), one patient had uncertain resection margins. Sensitivity of FDG-PET/MRI in detecting recurrence was 94%, specificity 94%, positive/negative predictive value and accuracy were 97%, 90% and 94%, respectively.

CONCLUSIONS

FDG-PET/MRI is a valuable tool in the diagnosis and staging of pelvic recurrence in patients with rectal cancer.

KEY POINTS

• Metabolic information obtained from PET coupled with excellent soft tissue contrast from MRI could facilitate detection of rectal cancer recurrence and assist in treatment planning. • PET/MRI demonstrates high sensitivity and specificity for the diagnosis of local recurrence of rectal cancer • PET/MRI led to alterations in management in 18.2% of patients.